This invention relates to an electrical rotary switch for several switch positions having a control knob mounted in a housing supported on one side, or on two sides, by three ball bearings that, guided by a cage disk, roll in a housing groove formed by an axial wall and a radial wall against which the ball bearings are loaded under the pressure of an outer or inner conical bearing surface of the control knob, whereby the axial--and radial-wall bearing surfaces respectively have contact segments and contact bands thereon that extend out of the housing via terminal lugs and are shorted by a first of the ball bearings in predetermined switch positions.
German patent document (DE 197 20 544. 4), for example, which has not previously been published, discloses a rotary switch of this type having circularly-arranged contacts in a base unit.
This rotary switch provides a compact structure with sensitive adjustment, having a sufficiently large adjustment range of the control knob, which is based on the principle that a ball or roller on which an object rolls, rolls at half the speed of the object, and travels only half the distance. In the described embodiment of a rotary switch, a step down is achieved from the actuating movement of the control knob to displacement of ball bearings, and to displacement of a cage guiding the ball bearings, without, for example, requiring toothed gearing. Since ball bearings have only one point of contact to their supports, current flowing through the ball bearings is limited. There arises, therefore, a need, in order to achieve given sensitive adjustments, to also be able to switch-in greater currents, particularly in a last position of a step switch.
Accordingly, it is an object of the invention to provide a rotary switch of the type set forth in the opening paragraph above which has a sensitive adjustment and an increased switching current.